Catalytic oxidation reactor with enhanced heat exchanging system

ABSTRACT

A heat exchange-type reactor includes a reaction chamber ( 1 ) having mounted therein a plurality of contact tubes ( 5 ) filled with a catalyst material; at least one shield plate ( 11 ) mounted within the reaction chamber to partition an inner space of the reaction chamber into at least two separate spaces ( 1   d,    1   e ); a plurality of conduits ( 13, 15, 17, 19 ) having entrance ( 15   a,    17   a ) and exit ( 13   a,    17   a ) openings through which a heat transfer medium respectively enters and exits, and being mounted to an outer circumference of the reaction chamber ( 1 ) corresponding to the partitioned spaces ( 1   d,    1   e ); and a heat exchange unit connected to the conduits ( 13, 15, 17, 19 ) to perform heat exchange of the heat transfer medium, in which the heat exchange unit includes a single heat exchanger that performs the exchange of heat of the heat transfer medium in accordance with the partitioned spaces.

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a heat exchange-type reactor,and more particularly, to a heat exchange-type reactor used to produceacrylic acid by utilizing a catalytic oxidation reaction.

[0003] (b) Description of the Related Art

[0004] Acrylic acid is typically produced from propylene that hasundergone a two-stage vapor phase catalytic oxidation reaction. In thefirst stage, molecular oxygen, diluted inert gas, steam, and apredetermined amount of a catalyst to oxidize propylene to therebyproduce acrolein is used. In the second step, molecular oxygen, dilutedinert gas, vapor, and a predetermined amount of a catalyst to oxidizeacrolein is again used to thereby produce acrylic acid.

[0005] A reactor performing these processes is configured to performboth stages in a single device or to perform the two stages in twodifferent devices. U.S. Pat. No. 4,256,783 discloses such a reactor.

[0006] In industries that use such reactors, much effort is being putforth to increase manufacturing productivity by improving the structureof the reactor, providing an optimal catalyst to bring about theoxidation reaction, or by improving the driving of the processes, etc.In this regard, a space velocity of propylene supplied to the reactor orthe concentration of the propylene is increased. In either of these twocases, the oxidation reaction in the reactor abruptly occurs such thatit is difficult to control the reaction temperature, and in addition,many hot spots are generated in catalyst layers of the tubular reactorsuch that by-products such as carbon monoxide and carbon dioxide areproduced to thereby reduce the yield of the acrylic acid. Further, whenproducing acrylic acid that uses a high space velocity and a highconcentration of propylene, the accelerated exothermic reactions causedifficulty in controlling reaction temperature. As a result, a problemwith the catalyst layer occurs (e.g., a reduction in the number ofactive sites caused by a breakaway of effective elements and a sinteringof metal elements) such that its function deteriorates.

[0007] Hence, during the manufacture of acrylic acid, controlling theheat in the reactor is the most important aspect for ensuring highproductivity. In particular, it is necessary to minimize temperatures atthe hot spots in the catalyst layers and heat accumulation in thevicinity of the hot spots, and to eliminate runaway of the reactorcaused by the hot spots (runaway is a situation in which the heatgeneration reaction becomes excessive so that the reactor cannot becontrolled or the reactor explodes).

[0008] To remedy such problems, U.S. Pat. No. 4,256,783 is structuredsuch that a shield plate is mounted in a shell of a reactor thatprovides a plurality of tubes. The shield plate divides the space withinthe shell such that the temperature in the resulting separate spaces maybe controlled according to different temperature distributions.

[0009] In addition to the above patent, configurations to obtaineffective cooling systems are disclosed, in which molten saltcirculation paths for the mounting of various baffles (e.g., U.S. Pat.No. 3,871,445), and an oxidation reactor design that combines a coolerand a heat exchanger (e.g., U.S. Pat. No. 3,147,084) are provided.

[0010] However, in such reactors, although the management of hot spotsin the catalyst layers by the shield plate is more effectively realized,since a separate heat exchanger is required for each of the dividedspaces in the shell, the overall structure of the device becomes morecomplicated.

SUMMARY OF THE INVENTION

[0011] It is one object of the present invention to provide a heatexchange-type reactor, in which the temperatures at the hot spots areeffectively controlled and runaway may be avoided, and in which astructure of a heat exchanging system corresponding to divided spaceswithin a shell is simplified.

[0012] In one embodiment, the present invention provides a heatexchange-type reactor including a reaction chamber having mountedtherein a plurality of contact tubes filled with catalyst materials; atleast one shield plate mounted within the reaction chamber to partitionan inner space of the reaction chamber into at least two separatespaces; a plurality of pairs of conduits having entrance and exitopenings through which a heat transfer medium respectively enters andexits, and being mounted to an outer circumference of the reactionchamber corresponding to the partitioned spaces; and a heat exchangeunit connected to the conduits to perform heat exchange of the heattransfer medium, wherein the heat exchange unit includes a single heatexchanger that performs the exchange of heat of the heat transfer mediumin accordance with the partitioned spaces. The molten salts, siliconeoils, DOWTHERMs, steam and the like may be used as the heat transfermedium.

[0013] The heat exchange unit connects the heat exchanger to one of theconduits having an exit opening, and the heat exchange unit includes afirst holder connected to a conduit having an entrance opening and toanother conduit having an exit opening, a steam line being connected tothe first holder to heat the heat transfer medium; a second holderconnected to the heat exchanger and to another conduit having anentrance opening to receive the heat transfer medium that has undergoneheat exchange through the heat exchanger; and a regulating valveconnected between the first holder and the second holder, the regulatingvalve regulating a flow rate of the heat transfer medium between the twoholders.

[0014] In another aspect, the heat exchange unit includes a third holderconnected to a conduit having an entrance opening and to which isconnected a steam line to heat the heat transfer medium; a fourth holderconnected to a conduit having an entrance opening and to which isconnected a steam line to heat the heat transfer medium; a first 4-wayvalve connected to another conduit having an exit opening and to theheat exchanger; a second 4-way valve connected to the heat exchanger andto the third and fourth holders; and a regulating valve connectedbetween the third holder and the fourth holder, the regulating valveregulating a flow rate of the heat transfer medium received in thefourth holder.

[0015] In particular, it is desirable that the entrance openings of theconduits are implemented closer to the shield plate than the exitopenings of the conduits, and the heat transfer medium is molten salt.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate an embodiment of theinvention, and, together with the description, serve to explain theprinciples of the invention.

[0017]FIG. 1 is a typical view of a catalytic oxidation reactoraccording to a first embodiment of the present invention.

[0018]FIG. 2 is a sectional view of a first reaction chamber of thecatalytic oxidation reactor of FIG. 1.

[0019]FIG. 3 is a sectional view of a second reaction chamber of thecatalytic oxidation reactor of FIG. 1.

[0020]FIG. 4 is a drawing used to describe an operation of a heatexchange unit of the catalytic oxidation reactor of FIG. 1.

[0021]FIG. 5 is a typical view of a catalytic oxidation reactoraccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Preferred embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings.

[0023]FIG. 1 is a typical view of a catalytic oxidation reactoraccording to a first embodiment of the present invention, and FIGS. 2and 3 are sectional views of reaction chambers of the catalyticoxidation reactor.

[0024] The reactor is a heat exchange-type reactor used for producingacrylic acid from propylene. With reference to the drawings, the reactoraccording to a first embodiment of the present invention includesreaction chambers 1 and 3. That is, since acrylic acid is produced byperforming an oxidation reaction in two stages in the first embodiment,the reactor includes a first reaction chamber 1 and a second reactionchamber 3 connected in series. A first oxidation reaction is performedin the first reaction chamber 1 and a second oxidation reaction isperformed in the second reaction chamber 3. The first reaction chamber 1includes a cylindrical shell 1 a of a predetermined size that defines aninner space, and an upper cap 1 b and a lower cap 1 c connected toopposite ends of the shell 1 a (i.e., to upper and lower ends of theshell 1 a in the drawing). Similarly, the second reaction chamber 3includes a cylindrical shell 3 a of a predetermined size that defines aninner space, and an upper cap 3 b and a lower cap 3 c connected toopposite ends of the shell 3 a (i.e., to upper and lower ends of theshell 3 a in the drawing).

[0025] A plurality of contact tubes 5 are mounted at predeterminedintervals in the first and second reaction chambers 1 and 3. The contacttubes 5 are filled with catalyst materials. Further, donut-shapedbaffles 7 or disc-shaped baffles 9 are mounted in the first and secondreaction chambers 1 and 3. The baffles 7 and 9 guide the flow of a heattransfer medium that is circulated within the first and second reactionchambers 1 and 3.

[0026] Also mounted in each of the first and second reaction chambers 1and 3 is at least one shield plates 11. The shield plates 11 of thefirst and second reaction chambers 1 and 3 partition the spaces definedtherein into at least two separate spaces. In the first preferredembodiment of the present invention, one shield plate 11 is provided ineach of the first and second reaction chambers 1 and 3 to divide thespaces therein into two separate spaces, that is, spaces 1 d and 1 e forthe first reaction chamber 1 and spaces 3 d and 3 e for the secondreaction chamber 3.

[0027] Mounted to an outer circumference of the first reaction chamber 1for the flow of a heat transfer medium (hereinafter referred to asmolten salt since this is the material used in the first preferredembodiment) are conduits 13, 15, 17, and 19, and to a circumference ofthe second reaction chamber 3 for the flow of molten salt are conduits21, 23, 25, and 27. In the first preferred embodiment of the presentinvention, the conduits 13, 15, 17, 19, 21, 23, 25, and 27 arering-shaped to correspond to the cylindrical outer shape of the shells 1a and 3 a respectively of the first and second reaction chambers 1 and3, and are structured to either supply molten salt flowing therein intothe first and second reaction chambers 1 and 3 or to discharge themolten salt from within the first and second reaction chambers 1 and 3.

[0028] The molten salt flows into or out of the conduits 13, 15, 17, 19,21, 23, 25, and 27 from or to heat exchange units 29 and 31, which aremounted external to the first and second reaction chambers 1 and 3. Torealize this operation, the conduits 15, 17, 23, and 25 respectivelyinclude entrance openings 15 a, 17 a, 23 a, and 25 a, while the conduits13, 19, 21, and 27 respectively include exit openings 13 a, 19 a, 21 a,and 27 a.

[0029] As shown in the drawings, the conduits 13, 15, 17, 19, 21, 23,25, and 27 are provided in pairs that correspond to the spaces 1 d, 1 e,3 d, and 3 e of the first and second reaction chambers 1 and 3. Theconduits 15, 17, 23, and 25 respectively including the entrance openings15 a, 17 a, 23 a, and 25 a are positioned closer to the shield plates 11than the conduits 13, 19, 21, and 27 respectively including the exitopenings 13 a, 19 a, 21 a, and 27 a.

[0030] The heat exchange units 29 and 31 perform heat transfer operationby using the molten salt. That is, the heat exchange units 29 and 31either increase or decrease the temperature of the molten salt dependingon a location of the contact tubes 5 along the axis Z direction of thefirst and second reaction chambers 1 and 3. In the first embodiment ofthe present invention, the heat exchange units 29 and 31 respectivelyinclude heat exchangers 29 a and 31 a (i.e., a single heat exchangereach) that perform a heat exchange operation with the molten salt in thespaces 1 d, 1 e, 3 d, and 3 e of the first and second reaction chambers1 and 3.

[0031] Reference numerals I, II, III, and IV in FIG. 2 indicate thecatalyst or the inert particle layers classified according to oxidationreaction steps taking place in the reactors. For convenience, layer I isreferred to as an inert particle layer A, layer II is referred to as afirst stage layer A, layer III is referred to as a first stage layer B,and layer IV is referred to as an inert particle layer B. Since theaccumulation of heat is most severe in the vicinity of overheating spotsor hot spots in layer II, it is necessary that the molten salt that willbe circulated through layer II has the lowest catalyst activationtemperature. Also, since it is necessary that an oxidation reactionvigorously occurs in layer III, the molten salt must be circulatedthrough layer III at a higher temperature than when circulated throughlayer II. The different, relative temperatures of the molten saltaccording to the layer were obtained from the results of repeatedexperiments. In particular, it is preferable that the temperaturedifference in the molten salt between layer II and layer III is 0˜50°C., and more preferably 5˜20° C.

[0032] The heat exchange units 29 and 31 will now be described indetail. In the preferred embodiment of the present invention, the heatexchange units 29 and 31 each include a single heat exchanger asdescribed above, that is, the heat exchangers 29 a and 31 a,respectively. However the structures of these heat exchanging units neednot be limited to any particular configuration if each heat exchangingunit is organized so that the temperature of the molten salt circulatingech chamber can be properly controlled with one heat exchanger perchamber.

[0033] That is, in the first embodiment of the present invention, theheat exchange units 29 and 31 are realized through two differentconfigurations. First, the heat exchanger 29 a of the heat exchange unit29 corresponding to the first reaction chamber 1 is connected to theexit opening 13 a of the conduit 13, which is mounted corresponding tothe location of the space 1 d of the first reaction chamber 1. Further,the heat exchange unit 29 includes a first holder 29 c to which a steamline 29 b is connected. The first holder 29 c is connected to theentrance opening 15 a of the conduit 15, which is mounted correspondingto the location of the space 1 d of the first reaction chamber 1, and tothe exit opening 19 a of the conduit 19, which is mounted correspondingto the location of the space 1 e of the first reaction chamber 1.

[0034] The heat exchange unit 29 also includes a second holder 29 d thatis connected to the entrance opening 17 a of the conduit 17, which ismounted corresponding to the location of the space 1 e of the firstreaction chamber 1, and to the heat exchanger 29 a. A regulating valve29 e is mounted between and connected to the first holder 29 c and thesecond holder 29 d. The regulating valve 29 e detects a temperature ofthe molten salt circulating through the space 1 e of the first reactionchamber 1, and if needed operates such that a predetermined amount ofmolten salt stored in the first holder 29 c is transmitted to the secondholder 29 d.

[0035] The heat exchange unit 31, which operates in the second stage ofthe oxidation reaction, is structured to function differently from theheat exchange unit 29. The heat exchange unit 31 selectively realizescooling of the molten salt with respect to the spaces 3 d and 3 e of thesecond reaction chamber 3. In more detail, the heat exchange unit 29corresponding to the first reaction chamber 1 has a fixed structurewhere the molten salt with respect to the space 1 d is circulated at ahigher temperature than the molten salt in the space 1 e. On the otherhand, the heat exchange unit 31 has more flexible heat controllingstructure. That is, the heat exchange unit 31 corresponding to thesecond reaction chamber 3 is structured such that the temperatures ofthe molten salt in the spaces 3 d and 3 e may be selectively controlledif needed.

[0036] The heat exchange unit 31 includes the single heat exchanger 31a, as well as third and fourth holders 31 d and 31 e to which areconnected steam lines 31 b and 31 c, respectively. The third holder 31 dis connected to the entrance opening 23 a of the conduit 23, which ismounted corresponding to the location of the space 3 d of the secondreaction chamber 3, and the fourth holder 31 e is connected to theentrance opening 25 a of the conduit 25, which is mounted correspondingto the location of the space 3 e of the second reaction chamber 3.

[0037] The heat exchange unit 31 also includes first and second 4-wayvalves 31 f and 31 g. The first 4-way valve 31 f is connected to theexit opening 27 a of the conduit 27, which is mounted corresponding tothe location of the space 3 e of the second reaction chamber 3, and tothe exit opening 21 a of the conduit 21, which is mounted correspondingto the location of the space 3 d of the second reaction chamber 3. Onthe other hand, the second 4-way valve 31 g is connected to the heatexchanger 31 a and the fourth holder 31 e as well as to the first 4-wayvalve 31 f. In addition, the heat exchange unit 31 includes a regulatingvalve 31 h mounted between the third holder 31 d and the fourth holder31 e. The regulating valve 31 h detects a temperature of the molten saltcirculating through the space 3 d of the second reaction chamber 3, andif needed operates such that a predetermined amount of molten saltstored in the fourth holder 31 e is transmitted to the third holder 31d.

[0038] In FIG. 1, reference numeral 33 indicates a mixer that mixesmolecular oxygen, steam, inert gas, etc. supplied from separateentrances; reference numeral 35 indicates a mixer that mixes propylene,which is the main reactant, and a mixture supplied from the mixer 33;and reference numeral 37 indicates a mixer that mixes a reactantproduced after the first oxidation reaction in the first reactionchamber 1, a mixed gas that includes molecular oxygen, steam, etc.

[0039] With the heat exchange-type reactor of the first embodiment ofthe present invention structured as described above, the cooling of themolten salt is realized as follows during the production of acrylicacid, which occurs by propylene passing and reacting through the firstand second reaction chambers 1 and 3 by the operation of the heatexchange units 29 and 31 as will be described below.

[0040] In the following, since the overall processes involved in theproduction of acrylic acid by a catalytic oxidation reaction are wellknown, the following will mainly explain the operation of the heatexchange units 29 and 31 of the first preferred embodiment of thepresent invention.

[0041] First, a main reactant is supplied to the first reaction chamber1 through the mixer 35, and undergoes an oxidation reaction with theother reactants mentioned above in the first reaction chamber 1. Duringthe course of the reaction the molten salt is supplied to the space 1 dof the first reaction chamber 1 from the first holder 29 c to circulatethrough the space 1 d. Next, the molten salt exits the space 1 d to betransmitted to the heat exchanger 29 a.

[0042] The molten salt transmitted to the heat exchanger 29 a generatessteam while passing through the heat exchanger 29 a. Accordingly, thetemperature of the molten salt is lowered, and this cooled molten saltis supplied to the space 1 e, which requires a lower cooling temperaturedistribution than the space 1 d. This molten salt is circulated withinthe first reaction chamber 1 and then transmitted to the first holder 29c. During this process, the molten salt starting toward the space 1 dfrom the second holder 29 d receives a small amount of the molten saltin the first holder 29 c by the operation of the regulating valve 29depending on the temperature distribution in the space 1 d, such thatthe temperature of the molten salt directed toward the space 1 d isadjusted to a suitable level.

[0043] Through these processes, even if the heat exchange unit 29 hasonly the single heat exchanger 29 a, the temperature distribution of themolten salt with respect to the space within the first reaction chamber1, which requires differential temperature controlling, can beefficiently varied for supply to the first reaction chamber 1.

[0044] Acrolein produced after undergoing the first stage catalyticoxidation reaction through the first reaction chamber 1 and the heatexchange unit 29 is then supplied to the second reaction chamber 3 torealize a final production of acrylic acid by the catalytic oxidationreaction in the second reaction chamber 3. At this time, the molten saltcirculated in the second reaction chamber 3 undergoes heat exchangethrough the heat exchange unit 31 as follows.

[0045] It is necessary that molten salt circulated through the space 3 dof the second reaction chamber 3 has a lower temperature than moltensalt circulated through the space 3 e. Accordingly, molten salt suppliedto the space 3 e from the fourth holder 31 e is maintained at a fixedtemperature by the influence of the steam line 31 c mounted to thefourth holder 31 e while circulating through the space 3 d.Subsequently, the molten salt is supplied to the heat exchanger 31 a viathe first 4-way valve 31 f. At this stage, the molten salt generatessteam by the heat exchanger 31 a to thereby result in a reduction of itstemperature.

[0046] This cooled molten salt is then transmitted to the third holder31 d through the second 4-way valve 31 g, then to the space 3 d tocirculate therein. At this time, the molten salt in the fourth holder 31e is supplied to the third holder 31 d as needed by operation of theregulating valve 31 h such that molten salt of an optimal temperaturedistribution is circulated in the space 3 d.

[0047] Therefore, even if the heat exchange unit 31 has only the singleheat exchanger 31 a, the temperature of the molten salt may be reducedin accordance with the space of the second reaction chamber 3 that isdivided into upper and lower portions. If needed, the heat exchange unit31 may effectively control the temperature of the molten salt even inthe case where the temperature distributions of the molten saltcirculated through the spaces 3 d and 3 e are varying.

[0048] In particular, if the temperature of the molten salt circulatingthrough the space 3 e must be reduced below the temperature of themolten salt circulating through the space 3 d, the heat exchange unit 31operates as follows.

[0049] Referring to FIG. 4, the molten salt in the third holder 31 dheated by the steam line 31 b is supplied to the space 3 d of the secondreaction chamber 3 to be circulated therein. Next, the molten saltenters the heat exchange unit 31 a through the first 4-way valve 31 f.Further, the molten salt passed through the heat exchanger 31 agenerates steam therein such that its temperature is reduced. The cooledmolten salt passes through the second 4-way valve 31 g for supply to thefourth holder 31 e, after which the molten salt enters the space 3 e ofthe second reaction chamber 3 for circulation therein.

[0050] In the case where the temperature of the molten salt supplied tothe space of the second reaction chamber 3 must be varied, the pathwaysthat the molten salt travels may be altered by the operation of thefirst and second 4-way valves 31 f and 31 g. As a result, the moltensalt may be made to efficiently match the oxidation reaction conditionsand is supplied to the second reaction chamber 3. The implementation ofthe heat exchange unit 31, however, is not limited to the secondreaction chamber. If necessary, the same or the similar type of the heatexchange unit 31 can be installed for the first reaction chamber.

[0051]FIG. 5 is a typical view of a catalytic oxidation reactoraccording to a second embodiment of the present invention. As shown inthe drawing, the oxidation reactor according to the second embodiment ofthe present invention provides a single reaction chamber 50 to produceacrylic acid from propylene. That is, in the reaction chamber 50 bothfirst and second stage oxidation reactions occur. Heat exchange units 52are mounted to the reaction chamber 50, and the reactor includes all thestructural elements in the reaction chamber 50 as are provided in thefirst and second reaction chambers of the first preferred embodiment ofthe present invention.

[0052] The heat exchange units 52 have the structure of the heatexchange unit connected to the first reaction chamber of the firstembodiment. However, if needed, the heat exchange units 52 may bestructured similarly to the heat exchange unit connected to the secondreaction chamber of the first embodiment.

[0053] The operation of the reactor according to the second embodimentof the present invention is substantially identical to that of the firstembodiment. A detailed description of its operation will therefore notbe provided.

[0054] In the oxidation reactor of the present invention structured andoperating as described above, the configurations of the heat exchangeunits that operate to cool molten salt are simplified. Also, the coolingof the molten salt is effectively realized such that hot spots withrespect to the catalyst layer and runaway are minimized to greatlyimprove manufacturing productivity.

[0055] In addition, the oxidation reactor of the present inventiondecreases the number of heat exchangers for the heat exchange unitscorresponding to the reaction chamber, which has its inner spacedivided, such that overall manufacturing costs are reduced. Also, theoxidation reactor may cope with the situation in which the temperaturedistribution of the cooling layer within the reactor must be reversedwithout experiencing shutdown.

[0056] Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

What is claimed is:
 1. A heat exchange-type reactor, comprising: areaction chamber having a plurality of contact tubes filled withcatalyst materials mounted therein; at least one shield plate mountedwithin the reaction chamber to partition an inner space of the reactionchamber into at least two separate spaces; a plurality of conduitshaving entrance and exit openings through which a heat transfer mediumrespectively enters and exits, being mounted to an outer circumferenceof the reaction chamber corresponding to the partitioned spaces; and aheat exchange unit connected to the conduits to perform heat exchange ofthe heat transfer medium, wherein the heat exchange unit includes asingle heat exchanger that performs the exchange of heat of the heattransfer medium in accordance with the partitioned spaces.
 2. Thereactor of claim 1, wherein the heat exchange unit connects the heatexchanger to one of the conduits having an exit opening and comprises: afirst holder connected to a conduit having an entrance opening and toanother conduit having an exit opening, a steam line being connected tothe first holder to heat the heat transfer medium; a second holderconnected to the heat exchanger and to another conduit having anentrance opening to receive the heat transfer medium that has undergoneheat exchange through the heat exchanger; and a regulating valveconnected between the first holder and the second holder, the regulatingvalve regulating a flow rate of the heat transfer medium received in thesecond holder.
 3. The reactor of claim 1, wherein the heat exchange unitcomprises: a third holder connected to a conduit having an entranceopening and to which is connected a steam line to heat the heat transfermedium; a fourth holder connected to a conduit having an entranceopening and to which is connected a steam line to heat the heat transfermedium; a first 4-way valve connected to another conduit having an exitopening and to the heat exchanger; a second 4-way valve connected to theheat exchanger and to the third and fourth holders; and a regulatingvalve connected between the third holder and the fourth holder, theregulating valve regulating a flow rate of the heat transfer mediumreceived in the fourth holder.
 4. The reactor of claim 1, wherein theentrance openings of the conduits are closer to the shield plate thanthe exit openings of the conduits.
 5. The reactor of claim 1, whereinthe heat transfer medium is selected from the group consisting of moltensalts, silicone oils, DOWTHERMS and steam.